1. Technical Field
The present invention is related to a wiring substrate, more particularly, a high reliable substrate where the compression stress and tensile stress of an insulating layer formed on a substrate are constrained and the parasitic capacitance of wiring is partially constrained, electro optic circuit and electronic equipment using the wiring substrate.
2. Related Art
A wiring substrate using a conductive film is widely applied to various electronic equipment using electronic circuits and displays and various types if it are proposed. In many cases, such wiring substrate using a conductive film is provided with multiple layered wiring structures. Further, when supplying sufficient current to an element such as a display element, it is necessary to enlarge a wiring width and wiring thickness. Thus, an insulating layer of the substrate becomes thicker thereby. Thus, a substrate is happened to be bent and deformed by the compression stress and tensile stress of between insulating layers for multiple layers and an multiple wirings made of conductive films. This defect badly affects manufacturing processes and lowers quality and yield.
Further, even in an element in which a high speed driving is required because of the high performance of elements and a large sized wiring substrate, the above issue generates parasitic capacitance and wiring delay. In order to reduce this issue, the material for wiring is generally changed to low resistant or low dielectric (low-k) material. However, the cost for material is increased and the deformation of a substrate caused by film stress is revealed.
As a method of constraining bent of a wiring substrate, JA6-283859 suggests cooling with giving compressed stress to the horizontal direction of an insulating layer during the process of forming an insulating layer of the multi-layered wing.
However, in the case of JA 6-283859, even reducing the tensile stress of an insulating layer, it is difficult to arrange the compression stress at the time of cooling. If performing wrong arrangement, it causes insufficient reduction of the tensile stress and yielding the compression stress. Further, even when the stresses can be reduced during manufacturing, other stresses may yield by thermal expansion during using. It is extremely difficult to solve the issues of the stresses of an multi wirings and the delay of wirings at the same time.
If an insulating layer has thicker thickness as to constrain wiring capacitance of multi layer wirings, the stress of a substrate becomes large. When an wiring is formed on a glass or flexible substrate, it is necessary to make it endure tensile stress, compression stress, other stress and twist. Further, if a substrate having a large area is used, it is possible to yield indispensable twist and deformation of a substrate with tiny stresses.